A. Technical Field
The present invention relates to a process for inhibition of polymerization of a (meth)acrylate ester.
B. Background Art
In a process in which the reaction between (meth)acrylic acid and an alkylene oxide is carried out in the presence of a catalyst in order to produce a hydroxyalkyl (meth)acrylate, both the (meth)acrylic acid as a raw material and the hydroxyalkyl (meth)acrylate as the objective product have so polymerizable an unsaturated group as to easily polymerize due to such as light and heat. Therefore, it is important to inhibit their polymerization. General methods therefor involve using polymerization inhibitors, and the use of various polymerization inhibitors is attempted. Known as specific examples thereof are methods that involve using such as N-oxyl compounds and nitroso compounds. For example, JP-B-046496/1983 discloses a method that involves using an N-oxyl compound (e.g. 2,2,5,5-tetramethyl-3-oxopyrrolidine-1-oxyl and 2,2,6,6-tetramethyl-4-acetoxypiperidine-1-oxyl) as a polymerization inhibitor in order to inhibit the polymerization of α,β-unsaturated carboxylate esters. In addition, JP-A-194346/1993 discloses a method that involves using an N-nitroso-N-phenyl-N-hydroxylamine salt as a polymerization inhibitor in order to inhibit the polymerization of unsaturated monomers such as acrylic acid and esters thereof. Furthermore, Japanese Patent No. 2725638 proposes a method that involves using, together with the N-oxyl compound, at least one member selected from the group consisting of manganese salt compounds, copper salt compounds, 2,2,6,6-tetramethylpiperidine compounds, and nitroso compounds as polymerization inhibitors in order to inhibit the polymerization of (meth)acrylic acid and esters thereof.
However, even if these conventional polymerization inhibitors are added, there occur problems such that: while the hydroxyalkyl (meth)acrylate is distilled, a polymerized product is formed to result in the impossibility of the long-term operation of a production apparatus including a distillation column. Therefore, their effect of inhibition of polymerization has not been sufficient.